1. Susan was never one to follow the trends of the times just because everyone else did. You couldn’t accuse her of climbing on the bandwagon
2. The senator was a supporter of medical care for everyone in the country long before it became a popular cause. Now, however, everyone is jumping on the bandwagon

The expression is often uncomplimentary. A person who is described as climbing on the bandwagon has not joined the crowd out of commitment, but out of peer pressure.